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From: Cyrill Gorcunov on 10 Feb 2010 05:40
On 2/10/10, Peter Zijlstra <peterz(a)infradead.org> wrote:
> On Wed, 2010-02-10 at 01:39 +0300, Cyrill Gorcunov wrote:
>
>
>> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
>> =====================================================================
>> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event.c
>> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
>> @@ -26,6 +26,7 @@
>> #include <linux/bitops.h>
>>
>> #include <asm/apic.h>
>> +#include <asm/perf_p4.h>
>> #include <asm/stacktrace.h>
>> #include <asm/nmi.h>
>>
>> @@ -140,6 +141,7 @@ struct x86_pmu {
>> u64 max_period;
>> u64 intel_ctrl;
>> int (*hw_config)(struct perf_event_attr *attr, struct hw_perf_event
>> *hwc);
>> + int (*schedule_events)(struct cpu_hw_events *cpuc, int n, int *assign,
>> int cpu);
>> void (*enable_bts)(u64 config);
>> void (*disable_bts)(void);
>>
>
>> +/*
>> + * This is the most important routine of Netburst PMU actually
>> + * and need a huge speedup!
>> + */
>> +static int p4_pmu_schedule_events(struct cpu_hw_events *cpuc, int n, int
>> *assign, int cpu)
>> +{
>
>> +}
>
>
>> -static int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int
>> *assign)
>> +/* we don't use cpu argument here at all */
>> +static int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int
>> *assign, int cpu)
>> {
>> struct event_constraint *c, *constraints[X86_PMC_IDX_MAX];
>> unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
>
>
>> @@ -1796,7 +2305,7 @@ static int x86_pmu_enable(struct perf_ev
>> if (n < 0)
>> return n;
>>
>> - ret = x86_schedule_events(cpuc, n, assign);
>> + ret = x86_pmu.schedule_events(cpuc, n, assign, 0);
>> if (ret)
>> return ret;
>> /*
>
> This look like a bug, surely we can run on !cpu0.

Definitely! Thanks! It should be smp_processor_id()

>
>> @@ -2313,7 +2822,7 @@ int hw_perf_group_sched_in(struct perf_e
>> if (n0 < 0)
>> return n0;
>>
>> - ret = x86_schedule_events(cpuc, n0, assign);
>> + ret = x86_pmu.schedule_events(cpuc, n0, assign, cpu);
>> if (ret)
>> return ret;
>>
>
> I'd try BUG_ON(cpu != smp_processor_id()) and scrap passing that cpu
> thing around.
>

no, i need cpu to find out if event has migrated from other thread and
then i switch
some thread dependant flags in hw::config (ie escr and cccr), or i
miss something and events in one cpu just can't migrate to another
cpu?

>> @@ -2700,6 +3232,7 @@ static int validate_group(struct perf_ev
>> {
>> struct perf_event *leader = event->group_leader;
>> struct cpu_hw_events *fake_cpuc;
>> + int cpu = smp_processor_id();
>> int ret, n;
>>
>> ret = -ENOMEM;
>> @@ -2725,7 +3258,7 @@ static int validate_group(struct perf_ev
>>
>> fake_cpuc->n_events = n;
>>
>> - ret = x86_schedule_events(fake_cpuc, n, NULL);
>> + ret = x86_pmu.schedule_events(fake_cpuc, n, NULL, cpu);
>>
>> out_free:
>> kfree(fake_cpuc);
>
>
>
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From: Peter Zijlstra on 10 Feb 2010 06:00
On Wed, 2010-02-10 at 13:38 +0300, Cyrill Gorcunov wrote:
> > I'd try BUG_ON(cpu != smp_processor_id()) and scrap passing that cpu
> > thing around.
> >
>
> no, i need cpu to find out if event has migrated from other thread and
> then i switch
> some thread dependant flags in hw::config (ie escr and cccr), or i
> miss something and events in one cpu just can't migrate to another
> cpu?

Well, if we validate that cpu == smp_processor_id() (looking at
kernel/perf_event.c that does indeed seem true for
hw_perf_group_sched_in() -- which suggests we should simply remove that
cpu argument), and that cpu will stay constant throughout the whole
callchain (it does, its a local variable), we can remove it and
substitute smp_processor_id(), right?

As to migration of the event, its tied to a task, we're now installing
the event for a task it wouldn't make sense to allow that to be
preemptible.

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From: Cyrill Gorcunov on 10 Feb 2010 06:30
On 2/10/10, Peter Zijlstra <peterz(a)infradead.org> wrote:
> On Wed, 2010-02-10 at 13:38 +0300, Cyrill Gorcunov wrote:
>> > I'd try BUG_ON(cpu != smp_processor_id()) and scrap passing that cpu
>> > thing around.
>> >
>>
>> no, i need cpu to find out if event has migrated from other thread and
>> then i switch
>> some thread dependant flags in hw::config (ie escr and cccr), or i
>> miss something and events in one cpu just can't migrate to another
>> cpu?
>
> Well, if we validate that cpu == smp_processor_id() (looking at
> kernel/perf_event.c that does indeed seem true for
> hw_perf_group_sched_in() -- which suggests we should simply remove that
> cpu argument), and that cpu will stay constant throughout the whole
> callchain (it does, its a local variable), we can remove it and
> substitute smp_processor_id(), right?
>

yeah, seems so!

> As to migration of the event, its tied to a task, we're now installing
> the event for a task it wouldn't make sense to allow that to be
> preemptible.
>
>

ok, thanks for explanation, Peter! I'll take a closer look as only get
back from office.
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From: Peter Zijlstra on 11 Feb 2010 07:30
On Wed, 2010-02-10 at 11:52 +0100, Peter Zijlstra wrote:
> which suggests we should simply remove that cpu argument

The below patch does so for all in-tree bits.

Doing this patch reminded me of the mess that is
hw_perf_group_sched_in(), so I'm going to try and fix that next.

Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
---
arch/powerpc/kernel/perf_event.c | 10 +++++-----
arch/sparc/kernel/perf_event.c | 10 +++++-----
arch/x86/kernel/cpu/perf_event.c | 18 +++++++++---------
include/linux/perf_event.h | 2 +-
kernel/perf_event.c | 4 ++--
5 files changed, 22 insertions(+), 22 deletions(-)

Index: linux-2.6/arch/powerpc/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/perf_event.c 2010-02-11 13:06:35.769636948 +0100
+++ linux-2.6/arch/powerpc/kernel/perf_event.c 2010-02-11 13:06:42.709637562 +0100
@@ -718,10 +718,10 @@
return n;
}

-static void event_sched_in(struct perf_event *event, int cpu)
+static void event_sched_in(struct perf_event *event)
{
event->state = PERF_EVENT_STATE_ACTIVE;
- event->oncpu = cpu;
+ event->oncpu = smp_processor_id();
event->tstamp_running += event->ctx->time - event->tstamp_stopped;
if (is_software_event(event))
event->pmu->enable(event);
@@ -735,7 +735,7 @@
*/
int hw_perf_group_sched_in(struct perf_event *group_leader,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx, int cpu)
+ struct perf_event_context *ctx)
{
struct cpu_hw_events *cpuhw;
long i, n, n0;
@@ -766,10 +766,10 @@
cpuhw->event[i]->hw.config = cpuhw->events[i];
cpuctx->active_oncpu += n;
n = 1;
- event_sched_in(group_leader, cpu);
+ event_sched_in(group_leader);
list_for_each_entry(sub, &group_leader->sibling_list, group_entry) {
if (sub->state != PERF_EVENT_STATE_OFF) {
- event_sched_in(sub, cpu);
+ event_sched_in(sub);
++n;
}
}
Index: linux-2.6/arch/sparc/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/arch/sparc/kernel/perf_event.c 2010-02-11 13:06:35.779634028 +0100
+++ linux-2.6/arch/sparc/kernel/perf_event.c 2010-02-11 13:06:42.709637562 +0100
@@ -980,10 +980,10 @@
return n;
}

-static void event_sched_in(struct perf_event *event, int cpu)
+static void event_sched_in(struct perf_event *event)
{
event->state = PERF_EVENT_STATE_ACTIVE;
- event->oncpu = cpu;
+ event->oncpu = smp_processor_id();
event->tstamp_running += event->ctx->time - event->tstamp_stopped;
if (is_software_event(event))
event->pmu->enable(event);
@@ -991,7 +991,7 @@

int hw_perf_group_sched_in(struct perf_event *group_leader,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx, int cpu)
+ struct perf_event_context *ctx)
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
struct perf_event *sub;
@@ -1015,10 +1015,10 @@

cpuctx->active_oncpu += n;
n = 1;
- event_sched_in(group_leader, cpu);
+ event_sched_in(group_leader);
list_for_each_entry(sub, &group_leader->sibling_list, group_entry) {
if (sub->state != PERF_EVENT_STATE_OFF) {
- event_sched_in(sub, cpu);
+ event_sched_in(sub);
n++;
}
}
Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c 2010-02-11 13:06:42.699628399 +0100
+++ linux-2.6/arch/x86/kernel/cpu/perf_event.c 2010-02-11 13:06:42.719650288 +0100
@@ -2386,12 +2386,12 @@
}

static int x86_event_sched_in(struct perf_event *event,
- struct perf_cpu_context *cpuctx, int cpu)
+ struct perf_cpu_context *cpuctx)
{
int ret = 0;

event->state = PERF_EVENT_STATE_ACTIVE;
- event->oncpu = cpu;
+ event->oncpu = smp_processor_id();
event->tstamp_running += event->ctx->time - event->tstamp_stopped;

if (!is_x86_event(event))
@@ -2407,7 +2407,7 @@
}

static void x86_event_sched_out(struct perf_event *event,
- struct perf_cpu_context *cpuctx, int cpu)
+ struct perf_cpu_context *cpuctx)
{
event->state = PERF_EVENT_STATE_INACTIVE;
event->oncpu = -1;
@@ -2435,9 +2435,9 @@
*/
int hw_perf_group_sched_in(struct perf_event *leader,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx, int cpu)
+ struct perf_event_context *ctx)
{
- struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
+ struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
struct perf_event *sub;
int assign[X86_PMC_IDX_MAX];
int n0, n1, ret;
@@ -2451,14 +2451,14 @@
if (ret)
return ret;

- ret = x86_event_sched_in(leader, cpuctx, cpu);
+ ret = x86_event_sched_in(leader, cpuctx);
if (ret)
return ret;

n1 = 1;
list_for_each_entry(sub, &leader->sibling_list, group_entry) {
if (sub->state > PERF_EVENT_STATE_OFF) {
- ret = x86_event_sched_in(sub, cpuctx, cpu);
+ ret = x86_event_sched_in(sub, cpuctx);
if (ret)
goto undo;
++n1;
@@ -2483,11 +2483,11 @@
*/
return 1;
undo:
- x86_event_sched_out(leader, cpuctx, cpu);
+ x86_event_sched_out(leader, cpuctx);
n0 = 1;
list_for_each_entry(sub, &leader->sibling_list, group_entry) {
if (sub->state == PERF_EVENT_STATE_ACTIVE) {
- x86_event_sched_out(sub, cpuctx, cpu);
+ x86_event_sched_out(sub, cpuctx);
if (++n0 == n1)
break;
}
Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h 2010-02-11 13:06:35.799627560 +0100
+++ linux-2.6/include/linux/perf_event.h 2010-02-11 13:06:52.279636542 +0100
@@ -768,7 +768,7 @@
extern int perf_event_task_enable(void);
extern int hw_perf_group_sched_in(struct perf_event *group_leader,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx, int cpu);
+ struct perf_event_context *ctx);
extern void perf_event_update_userpage(struct perf_event *event);
extern int perf_event_release_kernel(struct perf_event *event);
extern struct perf_event *
Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c 2010-02-11 13:06:42.659637981 +0100
+++ linux-2.6/kernel/perf_event.c 2010-02-11 13:06:52.289627547 +0100
@@ -103,7 +103,7 @@
int __weak
hw_perf_group_sched_in(struct perf_event *group_leader,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx, int cpu)
+ struct perf_event_context *ctx)
{
return 0;
}
@@ -633,14 +633,13 @@
static int
event_sched_in(struct perf_event *event,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx,
- int cpu)
+ struct perf_event_context *ctx)
{
if (event->state <= PERF_EVENT_STATE_OFF)
return 0;

event->state = PERF_EVENT_STATE_ACTIVE;
- event->oncpu = cpu; /* TODO: put 'cpu' into cpuctx->cpu */
+ event->oncpu = smp_processor_id();
/*
* The new state must be visible before we turn it on in the hardware:
*/
@@ -667,8 +666,7 @@
static int
group_sched_in(struct perf_event *group_event,
struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx,
- int cpu)
+ struct perf_event_context *ctx)
{
struct perf_event *event, *partial_group;
int ret;
@@ -676,18 +674,18 @@
if (group_event->state == PERF_EVENT_STATE_OFF)
return 0;

- ret = hw_perf_group_sched_in(group_event, cpuctx, ctx, cpu);
+ ret = hw_perf_group_sched_in(group_event, cpuctx, ctx);
if (ret)
return ret < 0 ? ret : 0;

- if (event_sched_in(group_event, cpuctx, ctx, cpu))
+ if (event_sched_in(group_event, cpuctx, ctx))
return -EAGAIN;

/*
* Schedule in siblings as one group (if any):
*/
list_for_each_entry(event, &group_event->sibling_list, group_entry) {
- if (event_sched_in(event, cpuctx, ctx, cpu)) {
+ if (event_sched_in(event, cpuctx, ctx)) {
partial_group = event;
goto group_error;
}
@@ -761,7 +759,6 @@
struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
struct perf_event *leader = event->group_leader;
- int cpu = smp_processor_id();
int err;

/*
@@ -808,7 +805,7 @@
if (!group_can_go_on(event, cpuctx, 1))
err = -EEXIST;
else
- err = event_sched_in(event, cpuctx, ctx, cpu);
+ err = event_sched_in(event, cpuctx, ctx);

if (err) {
/*
@@ -950,11 +947,9 @@
} else {
perf_disable();
if (event == leader)
- err = group_sched_in(event, cpuctx, ctx,
- smp_processor_id());
+ err = group_sched_in(event, cpuctx, ctx);
else
- err = event_sched_in(event, cpuctx, ctx,
- smp_processor_id());
+ err = event_sched_in(event, cpuctx, ctx);
perf_enable();
}

@@ -1281,19 +1276,18 @@

static void
ctx_pinned_sched_in(struct perf_event_context *ctx,
- struct perf_cpu_context *cpuctx,
- int cpu)
+ struct perf_cpu_context *cpuctx)
{
struct perf_event *event;

list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
if (event->state <= PERF_EVENT_STATE_OFF)
continue;
- if (event->cpu != -1 && event->cpu != cpu)
+ if (event->cpu != -1 && event->cpu != smp_processor_id())
continue;

if (group_can_go_on(event, cpuctx, 1))
- group_sched_in(event, cpuctx, ctx, cpu);
+ group_sched_in(event, cpuctx, ctx);

/*
* If this pinned group hasn't been scheduled,
@@ -1308,8 +1302,7 @@

static void
ctx_flexible_sched_in(struct perf_event_context *ctx,
- struct perf_cpu_context *cpuctx,
- int cpu)
+ struct perf_cpu_context *cpuctx)
{
struct perf_event *event;
int can_add_hw = 1;
@@ -1322,11 +1315,11 @@
* Listen to the 'cpu' scheduling filter constraint
* of events:
*/
- if (event->cpu != -1 && event->cpu != cpu)
+ if (event->cpu != -1 && event->cpu != smp_processor_id())
continue;

if (group_can_go_on(event, cpuctx, can_add_hw))
- if (group_sched_in(event, cpuctx, ctx, cpu))
+ if (group_sched_in(event, cpuctx, ctx))
can_add_hw = 0;
}
}
@@ -1336,8 +1329,6 @@
struct perf_cpu_context *cpuctx,
enum event_type_t event_type)
{
- int cpu = smp_processor_id();
-
raw_spin_lock(&ctx->lock);
ctx->is_active = 1;
if (likely(!ctx->nr_events))
@@ -1352,11 +1343,11 @@
* in order to give them the best chance of going on.
*/
if (event_type & EVENT_PINNED)
- ctx_pinned_sched_in(ctx, cpuctx, cpu);
+ ctx_pinned_sched_in(ctx, cpuctx);

/* Then walk through the lower prio flexible groups */
if (event_type & EVENT_FLEXIBLE)
- ctx_flexible_sched_in(ctx, cpuctx, cpu);
+ ctx_flexible_sched_in(ctx, cpuctx);

perf_enable();
out:


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From: Cyrill Gorcunov on 11 Feb 2010 10:30
On Thu, Feb 11, 2010 at 01:21:58PM +0100, Peter Zijlstra wrote:
> On Wed, 2010-02-10 at 11:52 +0100, Peter Zijlstra wrote:
> > which suggests we should simply remove that cpu argument
>
> The below patch does so for all in-tree bits.
>
> Doing this patch reminded me of the mess that is
> hw_perf_group_sched_in(), so I'm going to try and fix that next.
>

Yes Peter, thanks! At least for me this patch makes code more
understandable :)

-- Cyrill
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